Since the time approximately 100 years ago when first technologies for wireless data transmission began to be employed, the bandwidth available for transmission has grown continuously. As is known, the width of the frequency band that can be used for transmission depends on the carrier frequency, so that as the frequency increases, the transmission bandwidths available also increase. Nowadays, carrier frequencies in the range from a few kilohertz to many gigahertz are used. Thus, so-called “wireless HD” operates with a carrier frequency of 60 GHz and bandwidths of 4 Gbit/s. In order to be able to achieve data rates in the range of 10 Gbit/s and higher, waves in the terahertz range will also be used as carriers in the future.
Such terahertz waves are generated by means of ultrafast electronic circuits or by means of optical methods. Since the electronic methods are limited in their speed on account of the lifetimes of free electrons and holes, these methods operate only inefficiently, if at all, at frequencies above 100 GHz. In contrast, the prior art optical methods for generating terahertz waves mostly employ high frequencies that are then reduced by frequency mixing.
For data transmission with terahertz waves, it is virtually essential that the carrier frequency can be reproduced with great accuracy. In this way, the receiver can produce a carrier wave of the same frequency that is then used for demodulating the incident wave. Uncontrollable variations over time in the fundamental frequency of the carrier wave hinder data transmission, since the receiver must dynamically adjust itself to the particular emission frequency.